1. Field of the Invention
The present invention relates to an apparatus, system, and method of inspecting an image and a non-transitory recording medium storing an image inspection control program, and more specifically, to inspecting an image formed on a recording sheet having a previously printed image.
2. Description of the Related Art
Conventionally, inspection of printed matter is performed by human operators. In recent years, an inspection apparatus that automatically inspects printed matter is widely used, mainly in the field of offset printing. For example, a master image is generated by reading specific printed matter that is selected based on the image quality, as a reference image. The corresponding portions of the master image and a read image of printed matter are compared to determine, by the degree of difference therebetween, whether there is a defect in the printed matter.
The printing apparatus, such as electrophotographic apparatus, is widely used to print a small number of pages. For example, the printing apparatus may perform variable printing in which the contents to be printed differ in each page. In such case, comparing the printed matter, with the master image generated from the printed matter, would be inefficient. In view of this, a master image may be generated based on print data to be output as a printed image of printed matter, and compared with the printed image subjected for inspection.
In order to compare between the master image and the printed image subjected for inspection, the sizes and the positions of the images need to be matched. Japanese Patent Application Publication No. JP-2005-49212-A proposes a method of matching the position and the size of the images, in which the projection waveforms in the horizontal and vertical directions are generated and corrected such that the peaks of the waveforms match.
When the image is printed on a blank recording sheet, a read image obtained by reading the printed image can be compared with a master image to inspect the read image. In case of preprint printing, in which data of a variable image that varies from sheet to sheet is printed on a preprint sheet, that is, a recording sheet having a previously printed image (“preprint image”) such as rule lines or template statements, the read image cannot be simply compared with the master image. Since the read image includes the preprint image and the variable image, it cannot be simply compared with the master image generated based on the variable image data. Rather, the master image is generated by combining the variable master image and the preprint image, and compared with the read image. The preprint image used for generating the master image is obtained by reading the preprint sheet having no variable image printed thereon.